Resistor



Aug. 18, 194 N. E. LINDENBLAD RESISTOR Filed July 27, 1939 INVEN TOR. Nl?. LIN DENBLA D l 4/ A TTORNEY.

Patented Aug. 18, 1942 UNITED RESISTOR Nils E. Lindenblad, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application July 27, 1939, Serial No. 286,788

3 Claims.

This invention relates to new and novel resistors of small internal and stray capacitance which are particularly adapted to high frequency circuits.

This application is a continuation in part of my copending application Serial No. 110,415, filed November 12, 1936, which has now matured into Patent #2,215,184, issued Sept. 17, 1940.

An object of this invention is to simplify and improve small capacity resistors generally.

Another object of this invention is to increase the loading capability in general of resistors of low internal and stray capacitance, in other Words, to provide a resistor of low internal and stray capacitance with improved means of heat dispensation.

It can also be stated that by this invention, there is provided resistor units of small physical dimensions having low values of distributed capacitance and capacitance leakage to the surrounding supporting elements.

Thus, one of the objects of this invention is to provide a small resistor with increased cooling means so that it will be able to carry a higher current load. The gain from this procedure is then that the resistor can be made very small and thus have low internal as well as stray capacitance, which is an important feature in short wave or high frequency circuits, such as in resistance coupled amplifiers handling wide frequency bands. An increased capacitance effect will cause an increasing reactive (capacitively reactive) current to be introduced at the higher frequencies together with the current determined by the resistive values which will result in undesired distortion.

A feature of this invention is the placing of resistive material in an efficient electrical insulating and cooling medium to reduce the physical dimensions of the resistor.

Another feature of this invention is the method of making improved enclosed resistor units and also the means of sup orting and connecting them in a circulating fluid cooling system. The improved resistor of this invention may be used in the circuit of a high power, resistance coupled linear amplifier for very high frequencies in the order of 20,000,000 to 2,000,000 cycles. The

inherent capacitance of the ordinary resistor becomes a serious factor that must be reckoned with when used in high frequenc circuits.

The outstanding factors contributing to the undesired capacitance effects of resistors known in the prior art are the large physical dimenf stant of the mechanical support for the wires or resistance material.

There have been several methods suggested in the past to reduce the above mentioned factors to a fair minimum as, for example, by the use of materials having high heat resistivity and also by supporting the wires or resistive element by a minimum amount of insulating material and allowing air currents to freely circulate around the resistance wire; however, such methods are still unsatisfactory for the higher frequencies.

Briefly, by my invention I propose to greatly improve the low capacitance resistors known in the prior art by mounting the resistance element within a tube of very high grade insulating material which at the high frequencies has a minimum dielectric effect upon the capacitance. The resistance element may be either that of a coated film, a wire, or a filament; the resistivity of the material may be of a high or low value. The tube of insulating material has a physical length greater than the length of the resistance e1ement. The resistance element is placed within a circulating fluid system. By the term minimum dielectric effect I mean the use of a good dielectric material, that is, a material having a low dielectric loss, to mechanically support the resistive element so that the dielectric constant of the resistor portion of a high frequency circuit will be small and the losses low when the resistor is placed in high frequency circuits. Although a resistive element which is a conductor has only pure resistance when placed in a direct current circuit, when placed in a high frequency circuit, the resistor portion of the high frequency circuit has in addition to the resistance, a series inductance which is caused by the length of the conductor and also its shape. Likewise, in shunt with the resistance and the series inductance, there is a shunt capacitance, this capacitance being caused by the insertion of some form of mechanical support which in this invention is the glass tube 2, and therefore as it is desirable to keep the dielectric losses to a minimum, it becomes necessary to employ as little insulating material in the circuit as possible. Likewise, it is desirable to keep the dielectric constant of the material low so that the total dielectric effect is maintained at a minimum amount.

This invention will best be understood by referring to the accompanying drawing, in which:

Fig. 1 is a schematic diagram of a fluid circulating coil system;

Fig. 2 is a detailed view of the improved resistor element comprising a resistive coated insulated tube located within a tube of material having a minimum low dielectric constant at the high frequencies;

Fig. 3 is a plan view of Fig, 2;

Fig. 4 is a modification of Fig. 1 wherein the circulating coil system is located within a tank of circulating liquid.

Referring now in detail to Fig. l, a schematic diagram is shown of a symmetrical arrangement of two resistors located within a circulating fluid and electrical insulating system such as oil 30, or the like. The resistance element I is shown located concentrically within the tubes 2 which are of high grade insulating material having a minimum dielectric effect, such as Pyrex, glass, isolantite, etc. The insulating tubes 2 are secured to a mounting panel 3 by means of flanges 4 and are coupled to circulating metallic pipes 5 and 6 by means of coupling fittings l and 8. The upper pipe 5 is connected to the top of a fluid radiator 9 of copper, which is provided with cooling fins ID. This radiator can be additionally cooled by an external water circulating or refrigeration system, air blast, etc. The lower circulating pipe 6 is coupled to the radiator at a point I I. The other half of the symmetrically arranged cooling system is arranged similarly to that mentioned above, except that there is provided a tube I2 which is of necessity longer than section 5 due to the fact that it is located at a greater distance from the radiator 9. Likewise, at the lower portion of the radiator, a circulating tube I4 is connected to the lower portion of the insulating tube 2. A pump 3| for assisting the fluid circulation may be interposed between tubes 2 and radiators 9. A fan 26 directs a blast of cooling air on the fins H).

In Figs. 2 and 3, there is shown in detail the preferred embodiment of this invention wherein resistance element 1 is in the form of a thin metal coating located on the inner wall of an insulating cylindrical tube 2A which is located in the central portion of the inner wall of insulating tube 2. The ends of the coating IA terminate in a metal-like band which is connected to a hollow terminal stud 2! through which a wire 22 connects band 20 with terminals 2|. To protect the supporting and sealing tip 23, there is provided a metallic bell-like member 24. The terminal 2! is provided with suitable nuts 25 and washers 26. To provide fluid tight connections to the insulating tube 2, there is provided in each end of the tube a series of grooves l9 to which any suitable coupling fitting is fastened such as rubber hose with metallic bands surrounding the grooved portion [9. A coated resistor is particularly valuable in circuits where a low inductive reactance is desirable. The coating of the resistormay, of course, be on either or both sides of a strip or on the inside, outside or both of a cylinder. The cylinder may also be the resistance material, itself. The main feature is that they should be immersed in an eificient cooling insulating fluid medium so that the physical dimensions of the resistor may be reduced.

As shown by Fig. 4 a radiator tank 20 may be more or less integral with the panel 3 of the set. As shown by Fig. 1, the lower circulating pipes 6 and M are each provided with a pump 3|. The radiator may also be cooled by an external water circulating system wherein the tank contains a circulating fluid, such as water 4| or the like which may be circulated by a pump 42. Radiator 9 is supported in the bottom of the tank by supports 43; to provide a fluid-tight container bushings 29 are provided.

Although only one fan or blower 26 for blowing a blast of cool air upon radiator 9 is shown, a greater member may be provided and arranged to cool any part of radiator 9, or fan 26 may be placed outside of tank 20 to provide additional cooling of the circulating fluid 2|.

I have found that thin coatings of a high resistance metal on glass or ceramic may be used for low power. However, when dealing with high power, resistors of this invention are desirable. Resistors made by depositing carbon on glass or ceramic cylinders through which water to be circulated when used as the center conductor of a section of concentric line are very satisfactory over quite a broad frequency band and will handle large amounts of power.

This invention is not to be limited to the modifications shown as it is evident to those skilled in the art that the invention may take other forms within the spirit and scope of the same, and therefore should not be limited except by such limitations as are imposed in the appended claims.

I claim:

1. A resistance for use in a high frequency circuit of a resistance coupled push-pull linear amplifier of a radio transmitter operated at frequencies in the order of 20,000,000 to 2,000,000 cycles, comprising a pair of non-inductive resistance units each including a first insulating tube having a metallic resistance coating, a pair of second insulating tubes each one surrounding one of said first tubes, a radiator having a nonconducting liquid located therein, means for placing said fluid in communication with said resistance coating and said radiator, said second pair of tubes being in fluid communication with said non-conducting liquid, a tank containing a second liquid, said radiator and a portion of said non-conducting liquid within said radiator, all located within said tank, and means external of said tank for circulating said second liquid to cool said radiator.

2. A high frequency circuit resistance comprising a first insulating tube, a metallic resistance coating located on the inside wall of said first insulating tube, a second insulating tube concentrically surrounding said first insulating tube, a fluid cooling system including a radiator, said second tube being in fluid communication with said fluid circulating system, and a pump connected in series with said second tube and said radiator, terminal means passing through the walls of said second tube, and a pair of metallic bands located on the ends of said first tube to contact said metallic resistance coating and connected to said terminal means, the ends of said second tube having mechanical coupling means for coupling said metallic resistance coating with said fluid circulating system to cool said resistance.

3. A resistance for use in a high frequency circuit comprising a first insulating tube, a metallic coating on the inside wall of said first insulating tube, a second insulating tube secured to and surrounding said first insulating tube, a tank forming a circulating fluid system including a fluid located within said tank, means for circulating said fluid, a radiator containing a non-conducting fluid forming another portion of said circulating system, said second tube being in fluid communication with the non-conducting fluid, said radiator being located within said tank, and means including a pump for circulating said non-conducting fluid.

NILS E. LINDENBLAD. 

